The goals of this program are aimed at a better understanding of bone development and remodeling, and the endocrine factors that influence bone, such as parathyroid hormone and calcitonin. Toward this end we are studying characteristic components of bone tissue, including citric acid, hyaluronic acid, alkaline phosphatases and prolyl hydroxylase, as well as the effects of certain vitamins and hormones on them. In addition, cell culture studies are now under way in an attempt to characterize the type of bone cell(s) that respond to these agents and the mechanisms which underlie the observed responses. These investigations will provide a clearer understanding of the biochemical events involved in such processes as bone resorption. We will continue as part of an overall program the studies on the biosynthesis of parathyroid hormone. These include both chemical and biological investigations which are aimed at understanding the mechanisms of prohormone conversion to hormone and its subsequent secretion by the gland. BIBLIOGRAPHIC REFERENCES: Luben, R.A. and Cohn, D.V: Effects of parathormone and calcitonin on citrate and hyaluronate metabolism in cultured bone. Endocrinology 98:413-419, 1976. Luben, R.A., Wong, G.L. and Cohn, D.V: Biochemical characterization with parathormone and calcitonin of isolated bone cells: Provisional identification of osteoclasts and osteoblasts. Endocrinology 99:526-534, 1976.